Lubricant composition for limiting friction

ABSTRACT

A lubricant composition comprising, in relation to the total weight of the lubricant composition:at least one base oil;0.005 to 10% by weight of at least one polymeric organic friction modifier; and0.005 to 10% by weight of at least one ester, said polymeric organic friction modifier being the reaction product of:a) at least one hydrophobic polymer subunit which comprises a hydrophobic polymer selected from polyolefins, polyacrylics and polystyrenes;b) at least one hydrophilic polymer subunit which comprises a hydrophilic polymer selected from polyethers, polyesters and polyamides;c) optionally at least one backbone moiety capable of linking polymeric subunits together; andd) optionally a chain termination group.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2020/085684 filed Dec. 11, 2020, which claims priority of French Patent Application No. 19 14389 filed Dec. 13, 2019. The entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present application relates to new lubricant compositions, in particular for reducing friction between mechanical parts, preferably between two parts of an engine, such as a vehicle engine. For example, the lubricant compositions according to the invention can be used to lubricate an internal combustion engine, in particular a vehicle engine, in particular a motor vehicle engine.

BACKGROUND

The purpose of lubricants is to reduce friction and wear of mechanical parts, especially in vehicle engines, and more particularly in motor vehicles.

To reduce these friction phenomena, it is known to incorporate friction modifiers in lubricants.

Among friction modifiers, organomolybdenum compounds represent a family of compounds whose friction-reducing properties have been widely described. However, it is known to the person skilled in the art that the use of organomolybdenum compounds, in particular organomolybdenum compounds comprising a dithiocarbamate group, can worsen the wearing of mechanical parts. Other solutions were then proposed to reduce friction between two mechanical parts.

Among these alternatives, polymeric organic friction modifiers are currently sometimes used. Polymeric organic friction modifiers include the reaction product of an optionally functionalized polyolefin, a polyether, a polyol and a carboxylic acid end group. WO2011/107739 describes polymeric organic friction modifiers.

This type of polymeric friction modifier makes it possible to achieve coefficients of friction between mechanical parts that are sometimes too high for the applications envisaged.

There is therefore a particular interest in the provision of lubricant compositions to reduce friction between mechanical parts.

SUMMARY

One objective of the present application is to provide lubricant compositions for reducing friction between mechanical parts.

Further objectives will become apparent from the following description of the invention.

DETAILED DESCRIPTION

These objectives are fulfilled by the present invention which provides a lubricant composition comprising, based on the total weight of the lubricant composition:

-   -   at least one base oil;     -   0.005 to 10% by weight of at least one polymeric organic         friction modifier; and     -   0.005 to 10% by weight of at least one ester which is a product         of the esterification reaction between a saturated or         unsaturated, linear, cyclic or branched monohydric alcohol         having 1 to 10 carbon atoms and a carboxylic polyacid or between         a linear, cyclic or branched polyol and a saturated or         unsaturated, linear, cyclic or branched monocarboxylic acid         having between 1 and 10 carbon atoms,     -   said polymeric organic friction modifier being the reaction         product of:     -   a) at least one hydrophobic polymer subunit which comprises a         hydrophobic polymer selected from polyolefins, polyacrylics and         polystyrenes;     -   b) at least one hydrophilic polymer subunit which comprises a         hydrophilic polymer selected from polyethers, polyesters and         polyamides;     -   c) optionally at least one backbone moiety capable of linking         polymeric subunits together; and     -   d) optionally a chain termination group.

More particularly, the inventors have surprisingly discovered that the combination of a polymeric organic friction modifier of the above type and an ester preferably selected from glycerol esters, citric acid esters, tartaric acid esters and mixtures thereof significantly improves the friction coefficient between mechanical parts.

Indeed, it has been discovered by the inventors that the ester chosen more particularly among glycerol esters, citric acid esters, tartaric acid esters and their mixture allows to boost surprisingly the effect of the polymeric organic friction modifier.

Preferably, the polymeric organic friction modifier has a weight average molecular weight of from 1000 to 30,000 Daltons, preferably from 1500 to 25,000 Daltons, advantageously from 2000 to 20,000 Daltons. The weight average molecular weight can be measured by steric exclusion chromatography.

According to one embodiment of the invention, the polymeric organic friction modifier is as defined in application WO2011/107739.

Preferably, the hydrophobic polymer subunit of the polymeric organic friction modifier comprises a hydrophobic polymer derived from a polymer of a mono-olefin comprising 2 to 6 carbon atoms, said mono-olefin preferably being selected from ethylene, propylene, butene and isobutene, more preferably being isobutene, and said polymer of a mono-olefin containing a chain of from 15 to 500, preferably from 50 to 200 carbon atoms

The hydrophilic polymer subunit of the polymeric organic friction modifier comprises a hydrophilic polymer selected from polyethers, polyamides and polyesters, preferably selected from polyethers.

The hydrophilic polymer subunit is preferably linear or branched.

The polyester is, for example, selected from polyethylene terephthalate, polylactide, and polycaprolactone.

The polyether is for example selected from polyglycerols and polyalkylene glycols.

According to a particularly preferred embodiment, the hydrophilic polymer subunit comprises a hydrophilic polymer which is a polymer of a water-soluble alkylene glycol. Preferably, the hydrophilic polymer subunit comprises a hydrophilic polymer which is a polyethylene glycol (PEG), preferably a PEG having a molecular weight ranging from 300 to 5,000 Daltons, advantageously ranging from 400 to 1,000 Daltons, in particular ranging from 400 to 800 Daltons.

For example, the hydrophilic polymer subunit comprises a hydrophilic polymer selected from PEG₄₀₀, PEG₆₀₀ and PEG₁₀₀₀

According to another embodiment, the hydrophilic polymer subunit comprises a poly(ethylene-propylene glycol) or poly(ethylene-butylene glycol) copolymer.

Alternatively, the hydrophilic polymer subunit comprises a hydrophilic polymer selected from polyethers and polyamides derived from diols and diamines, respectively, said diols and diamines containing at least one functional group selected from acid groups, e.g. carboxylic acid group, sulphonyl groups, e.g. sulphonylstyrene group, amine groups, e.g. tetraethylenepentamine (TEPA) or polyethyleneimine (PEI), and hydroxyl groups, e.g. sugar-based mono- or copolymers.

According to one embodiment, some of the hydrophobic polymer subunits and hydrophilic polymer subunits may be linked to form block copolymer units. The hydrophobic polymer subunits and hydrophilic polymer subunits capable of forming block copolymer units include functional groups that enable them to bind to each other.

Preferably, the hydrophobic polymer subunit comprises at least one diacid or anhydride group, said diacid or anhydride group being introduced into the hydrophobic polymer subunit by reaction with an unsaturated diacid or anhydride, for example maleic anhydride. The hydrophobic polymer subunit having at least one diacid or anhydride group is capable of reacting by esterification with a hydroxyl-terminated hydrophilic polymer subunit, for example a polyalkylene glycol.

Alternatively, the hydrophobic polymer subunit comprises at least one epoxide group, said epoxide group being introduced into the hydrophobic polymer subunit by an epoxidation reaction with a peracid, for example perbenzoic or peracetic acid. The hydrophobic polymer subunit having at least one epoxide group is capable of reacting with a hydrophilic hydroxyl—and/or acid-terminated polymer subunit.

In yet another embodiment, the hydrophobic polymer subunit has at least one unsaturated terminal, said unsaturated terminal being by esterification reaction between at least one hydroxyl group of the hydrophilic polymeric subunit and an unsaturated monocarboxylic acid, e.g. vinyl acids, in particular acrylic or methacrylic acid. The hydrophobic polymer subunit has at least one unsaturated terminal and is capable of free radical copolymerisation with a hydrophobic polyolefin polymer subunit.

Preferably, the hydrophobic polymer subunit comprises a polyisobutylene succinic anhydride (PIBSA), having a molecular weight ranging from 300 to 5000 Daltons, preferably ranging from 500 to 1500 Daltons, in particular ranging from 800 to 1200 Daltons. Polyisobutylene succinic anhydride is derived from the maleinisation of a polyisobutylene, in particular from the reaction between a polyisobutylene having an unsaturated terminal group and maleic anhydride.

The block copolymer units as described above are directly linked to each other.

Alternatively, the block copolymer units as described above are linked by the said at least one backbone moiety.

The backbone moiety is selected from polyols and polycarboxylic acids, preferably from polyols.

The polyol is selected from diols, triols, tetraols, dimers or trimers of diol, triol or tetraol and chain extended polymers of diol, triol or tetraol.

Preferably, the polyol is selected from glycerol, neopentyl glycol, trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerthyritol, dipentaerthyritol, tripentaerthyritol and sorbitol.

Advantageously, the polyol is glycerol.

The polycarboxylic acid is selected from dicarboxylic acids and tricarboxylic acids. Preferably, the polycarboxylic acid is a dicarboxylic acid, preferably a straight chain dicarboxylic acid, more preferably a dicarboxylic acid with a chain length between 2 and 10 carbon atoms.

Advantageously, the polycarboxylic acid is selected from oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and maleic acid.

Advantageously, the polycarboxylic acid is adipic acid.

Alternatively, the backbone moiety is selected from low molecular weight alkenylsuccinic anhydrides (ASA), preferably from C18 alkenylsuccinic anhydrides.

The choice of backbone moiety capable of linking the block copolymer units together is adapted depending on whether the linking of the units is between two hydrophobic polymer subunits, between two hydrophilic polymer subunits, or between a hydrophobic and a hydrophobic polymer subunit.

The backbone fragments included in the polymeric organic friction modifier are of the same or different nature.

The number of block copolymer units comprised in the polymeric organic friction modifier ranges from 1 to 20, preferably from 1 to 15, preferably from 1 to 10, advantageously from 1 to 7.

Where the reaction product for the production of the polymeric organic friction modifier is terminated by a reactive group (e.g. the hydroxyl groups of PEG), it may be desirable or useful in some circumstances to introduce a chain-terminating group at the end of the reaction product.

Preferably, the chain-terminating group is selected from fatty carboxylic acids, preferably from linear or branched, saturated or unsaturated C12-C22 acids, more preferably from lauric acid, erucic acid, isostearic acid, palmitic acid, oleic acid and linoleic acid, advantageously from palmitic acid, oleic acid and linoleic acid.

Preferably, the polymeric organic friction modifier used in the present invention has an acid number below 20, preferably below 15.

The reaction by which the polymeric organic friction modifier used in the present invention is produced is a single or multi-step process.

According to a specific embodiment, the polymeric organic friction modifier used in the present invention is the reaction product of a functionalized polyolefin, a polyether, a polyol and a carboxylic acid end group.

The lubricant composition according to the invention comprises from 0.005 to 10 wt %, preferably from 0.05 to 5 wt %, more preferably from 0.1 to 3 wt %, more preferably from 0.2 to 2 wt %, of polymeric organic friction modifier(s) as defined above, based on the total weight of the lubricant composition

The lubricant composition according to the invention comprises from 0.005 to 10% by weight, preferably from 0.05 to 5% by weight, preferably from 0.1 to 3% by weight, more preferably from 0.2 to 2% by weight, of at least one ester selected from glycerol esters, citric acid esters, tartaric acid esters, and mixtures thereof, based on the total weight of the lubricant composition.

The ester used according to the invention may be a mono-, di- or tri-ester. It can be a mixture of mono-, di- and/or tri-esters. Preferably, the ester used according to the invention comprises at least one triester.

Preferably, the ester is selected from glycerol esters, citric acid esters and mixtures thereof.

According to one embodiment of the invention, the glycerol ester is an ester of glycerol and a carboxylic acid having from 1 to 10 carbon atoms, preferably from 2 to 8 carbon atoms. Preferably, the carboxylic acid is a monocarboxylic acid. In one embodiment of the invention, the glycerol ester is selected from glycerol heptanoates and mixtures thereof.

The carboxylic acids used to prepare the glycerol ester are saturated or unsaturated, linear, cyclic or branched carboxylic acids, optionally substituted with hydroxyl and/or epoxy groups.

Preferably, the carboxylic acid used to prepare the glycerol ester is linear and saturated and has a hydrocarbon chain consisting of carbon and hydrogen atoms. In other words, according to a particular embodiment, the carboxylic acid used to prepare the glycerol ester does not comprise any heteroatoms other than those of the acid function.

In one embodiment, the glycerol ester is obtained from raw materials of renewable origin. The carboxylic acids that can be used to form the glycerol ester are, for example, carboxylic acids derived from vegetable oils, fats, of animal or vegetable origin, such as butyric acid, valeric acid, caproic acid, heptylic acid, caprylic acid, pelargonic acid, capric acid, crotonic acid, iso-crotonic acid, sorbic acid, isovaleric acid, taken alone or mixed. In another embodiment, the glycerol ester is obtained from raw materials of fossil origin. These are known as synthetic carboxylic acids. Synthetic carboxylic acids such as butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, taken alone or mixed, may also be used.

The glycerol esters used in the invention can be obtained by methods well known to the skilled person, for example by reacting carboxylic acids with glycerol. These chemical reactions, which are well known to the skilled person, can take place with or without a catalyst, with or without a solvent.

According to one embodiment, the glycerol ester used in the lubricant composition according to the invention is glycerol triheptanoate.

According to one embodiment, the tartaric acid ester is an ester of tartaric acid and an alcohol having from 1 to 10 carbon atoms, preferably from 2 to 8 carbon atoms. Preferably, the alcohol used to prepare the tartaric acid ester is a monoalcohol.

In one embodiment of the invention, the tartaric acid ester is selected from tartaric acid triesters.

According to one embodiment, the citric acid ester is an ester of citric acid and an alcohol having 1 to 10 carbon atoms, preferably 2 to 8 carbon atoms. Preferably, the alcohol used to prepare the citric acid ester is a monoalcohol.

In one embodiment of the invention, the citric acid ester is selected from citric acid triesters.

The alcohols used to prepare the citric acid ester or tartaric acid ester are saturated or unsaturated, linear, cyclic or branched alcohols, optionally substituted by acid and/or epoxy groups.

Preferably, the alcohol used to prepare the citric acid ester or tartaric acid ester is linear and saturated and has a hydrocarbon chain consisting of carbon and hydrogen atoms. In other words, according to a particular embodiment, the alcohol used to prepare the citric acid ester or tartaric acid ester does not comprise any heteroatoms other than those of the hydroxyl function.

The citric acid esters or tartaric acid esters used in the invention can be obtained by methods well known to the person skilled in the art, for example by reacting citric acid or tartaric acid with one or more alcohols. These chemical reactions, which are well known to the skilled person, can take place with or without a catalyst, with or without a solvent.

In one embodiment, the citric acid ester is selected from triethylcitrate, tributylcitrate and mixtures thereof.

According to an embodiment of the invention, the ester of the lubricant composition is selected from:

-   -   a triester of glycerol and of a monocarboxylic acid having from         1 to 10 carbon atoms, preferably from 2 to 8 carbon atoms; and     -   a triester of citric acid and of a monohydric alcohol having 1         to 10 carbon atoms, preferably 2 to 8 carbon atoms; and     -   mixtures thereof.

According to one embodiment of the invention, the ester of the lubricant composition is selected from glycerol triheptanoate, triethylcitrate, tributylcitrate and mixtures thereof.

The lubricant composition according to the invention comprises one or more base oils, preferably in an amount of at least 50% by weight, more preferably at least 60% by weight or even at least 70% by weight, based on the total weight of the lubricant composition.

The base oil(s) may be selected from the mineral, synthetic or natural, animal or vegetable lubricating base oils known to the skilled person.

The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origin belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (table 1) or mixtures thereof.

TABLE 1 Viscosity Saturated Sulphur index content content (VI) Grouping I <90% >0.03% 80 ≤ VI < 120 Mineral oils Grouping II ≥90% ≤0.03% 80 ≤ VI < 120 Hydrocracked oils Grouping III ≥90% ≤0.03% ≥120 Hydrocracked or hydro- isomerised oils Grouping IV Polyalphaolefins (PAO) Grouping V Esters, PAGs and other bases not included in Groupings I to IV

Mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, de-alkalization, solvent dewaxing, hydrotreating, hydrocracking, hydroisomerization and hydrofining.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases to make the lubricant compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulphur content, resistance to oxidation, suitable for their use.

The base oils of the lubricant compositions according to the invention may also be chosen from synthetic oils, such as certain esters of carboxylic acids and alcohols, and from polyalphaolefins. Polyalphaolefins used as base oils are for example obtained from monomers with 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100° C. is between 1.5 and 15 mm².s⁻¹ according to ASTM D445. Their average molecular weight is generally between 250 and 3,000 according to ASTM D5296.

According to one particular embodiment, the lubricant composition according to the invention comprises from 60% to 99.5% by weight of base oils, preferably from 70% to 99.5 by weight of base oils, relative to the total weight of the composition.

Many additional additives can be used for this lubricant composition according to the invention.

Preferred additional additives for the lubricant composition according to the invention are selected from detergent additives, anti-wear additives other than phospho-sulphur additives, friction modifying additives other than the polymeric organic friction modifiers defined above, extreme pressure additives, dispersants, pour point depressants, anti-foaming agents, thickeners and mixtures thereof.

Amine phosphates are anti-wear additives which can be used in the lubricant composition according to the invention. However, the phosphorus provided by these additives can act as a poison for automotive catalytic systems as these additives are ash generators. These effects can be minimised by partially substituting amine phosphates with non-phosphorous additives, such as polysulphides, especially sulphur-containing olefins.

Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 6 wt. %, preferably from 0.05 to 4 wt. %, more preferably from 0.1 to 2 wt. % based on the total weight of lubricant composition, anti-wear additives and extreme pressure additives.

Preferably, the lubricant composition according to the invention comprises, based on the total weight of lubricant composition:

-   -   at least 50% by weight, preferably at least 60% by weight, more         preferably 70% by weight, of one or more base oils;     -   from 0.005 a 10% by weight, preferably 0.05 to 5% by weight,         preferably from 0.1 to 3% by weight, more preferably from 0.2 to         2% by weight, of one or more polymeric organic friction         modifiers;     -   from 0.005 to 10% by weight, preferably from 0.05 to 5% by         weight, preferably from 0.1 to 3% by weight, more preferably         from 0.2 to 2% by weight, of one or more esters selected from         glycerol esters, citric acid esters, tartaric acid esters and         mixtures thereof;     -   optionally from 0.005 to 30% by weight, preferably from 0.1 to         25% by weight, more preferably from 1 to 20% by weight, of one         or more functional additives other than polymeric organic         friction modifiers and glycerol esters, citric acid esters and         tartaric acid esters preferably selected from detergent         additives, anti-wear additives other than phospho-sulphur         additives, friction modifying additives, extreme pressure         additives, dispersants, pour point depressants, anti-foaming         agents, thickeners and mixtures thereof.

Advantageously, the lubricant composition according to the invention may comprise at least one additional friction modifier additive different from the polymeric organic friction modifiers defined above. The additional friction modifier additive may be selected from a compound providing metallic elements and an ash-free compound. Among the compounds providing metallic elements, we can mention transition metal complexes such as Sb, Sn, Fe, Cu, Zn, Mo whose ligands can be hydrocarbon compounds comprising oxygen, nitrogen, sulphur or phosphorus atoms.

Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive.

The antioxidant additive generally delays the degradation of the lubricant composition in service. This degradation may result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

Antioxidant additives act as radical inhibitors or hydroperoxide destroyers. Commonly used antioxidant additives include phenolic antioxidant additives, amine antioxidant additives and phosphosulphur antioxidant additives. Some of these antioxidant additives, e.g. phosphosulphur antioxidant additives, can be ash-forming. Phenolic antioxidant additives can be ash-free or in the form of neutral or basic metal salts. The antioxidant additives may in particular be selected from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C1-012, alkyl group, N,N′-dialkyl-aryl-diamines and mixtures thereof.

Preferably according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon bearing the alcohol function is substituted by at least one C₁-C₁₀, alkyl group, preferably a C₁-C₆, alkyl group, preferably a C₄, alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, possibly in combination with phenolic antioxidant additives. Examples of amino compounds are aromatic amines, for example aromatic amines of the formula NR⁷R⁹R⁹ where R⁷ represents an aliphatic group or an aromatic group, optionally substituted, R⁸ represents an aromatic group, optionally substituted, R⁹ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R¹⁰S(O)_(z)R¹¹ in which R¹⁰ represents an alkylene group or an alkenylene group, R¹¹ represents an alkyl group, an alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulphurised alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

Another class of antioxidant additives are copper compounds, e.g. copper thio- or dithio-phosphates, copper salts of carboxylic acids, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper I and II salts, succinic acid or anhydride salts can also be used.

The lubricant composition according to the invention may contain any type of antioxidant additives known to the person skilled in the art.

Advantageously, the lubricant composition comprises at least one ash-free antioxidant additive.

Equally advantageously, the lubricant composition according to the invention comprises from 0.5 to 2% by weight, based on the total mass of the composition, of at least one antioxidant additive.

The lubricant composition according to the invention may also comprise at least one detergent additive.

Detergent additives generally reduce the formation of deposits on the surface of metal parts by dissolving oxidation and combustion by-products.

The detergent additives used in the lubricant composition according to the invention are generally known to the person skilled in the art. Detergent additives can be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali or alkaline earth metal.

The detergent additives are preferably selected from alkali or alkaline earth metals of carboxylic acids, sulphonates, salicylates, naphthenates, and phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally contain the metal in a stoichiometric amount or in excess, i.e. in an amount greater than the stoichiometric amount. These are overbased detergent additives; the excess metal giving the overbased character to the detergent is generally in the form of oil-insoluble metal salts, e.g. carbonate, hydroxide, oxalate, acetate, glutamate, preferably carbonate.

Advantageously, the lubricant composition according to the invention may comprise from 2% to 4% by weight of detergent additive relative to the total weight of the lubricant composition.

Equally advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive.

By slowing down the formation of paraffin crystals, pour point depressant additives generally improve the cold behaviour of the lubricant composition according to the invention.

Examples of pour point depressant additives are alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes, alkylated polystyrenes.

Advantageously, the lubricant composition according to the invention may also comprise at least one dispersing agent.

The dispersing agent may be selected from Mannich bases, succinimides and derivatives thereof.

Advantageously, the lubricant composition according to the invention may comprise from 0.2% to 10% by weight of dispersant(s) based on the total weight of the lubricant composition.

The lubricant composition of the present invention may also comprise at least one additional polymer that can improve the viscosity index. Examples of additional viscosity index improving polymers are polymeric esters, hydrogenated or non-hydrogenated homopolymers or copolymers of styrene, butadiene and isoprene, polymethacrylates (PMA).

The present invention also relates to the use of the lubricant composition as defined above for the lubrication of metal parts, in particular for the lubrication of engines, in particular internal combustion engines, for example vehicle engines.

Advantageously, the lubricant composition according to the invention makes it possible to reduce friction, in particular between two mechanical parts, for example two parts of an engine, in particular an internal combustion engine, for example a vehicle engine.

Thus, the invention relates to the use of the lubricant composition according to the invention to reduce the wear of mechanical parts, for example parts of an engine, in particular a vehicle engine.

The present application also relates to a method of lubricating mechanical parts, particularly in an engine, such as an internal combustion engine, comprising at least one step of bringing a part into contact with the lubricating composition according to the invention.

The present invention will now be described with the help of non-limiting examples.

Example 1: Lubricant Compositions

The compositions in Table 2 (LC: lubricant composition according to the invention; CC: comparative composition) were prepared by mixing at 60° C. the ester and/or polymeric friction modifier in a composition comprising base oil, viscosity index improver and additive package, to give the proportions shown in Table 2. The percentages shown are based on 100% by weight of the lubricant composition including the ester and/or polymeric friction modifier.

TABLE 2 Table 2. Lubricant compositions according to the invention and comparative ones Lubricant LC1 LC2 LC3 LC4 LC5 CC1 CC2 composition (% by weight) (% by weight) (% by weight) (% by weight) (% by weight) (% by weight) (% by weight) triethylcitrate 1 2 0.5 — — — 1 tributylcitrate — — — 1 — — Glycerol triheptanoate — — — 1 — — — Organic friction 0.5 0.5 0.25 0.5 0.5 0.5 — modifier according to the invention* Additive package 1** 13.3 12.3 14.05 13.3 13.3 14.3 13.8 Viscosity index 6.1 6.1 6.1 6.1 6.1 6.1 6.1 improver (olefin copolymer) Group III base oil 79.1 79.1 79.1 79.1 79.1 79.1 79.1 *An organic friction modifier according to the invention which is the reaction product of: a) a hydrophobic polymer subunit which comprises a hydrophobic polymer selected from polyolefins, polyacrylics and polystyrenes; b) a hydrophilic polymer sub-unit which comprises a hydrophilic polymer selected from polyethers, polyesters and polyamides; c) optionally at least one backbone moiety capable of linking polymeric subunits together; and d) optionally a chain termination group. **comprising detergents, dispersants, antioxidants and anti-wear agents

The compositions in Table 3 (LC: lubricant composition according to the invention; CC: comparative composition) were prepared by mixing at 60° C. the ester and/or polymeric friction modifier in a composition comprising base oil, viscosity index improver and additive package, to give the proportions shown in Table 3. The percentages shown are based on 100% by weight of the lubricant composition including the ester and/or polymeric friction modifier.

TABLE 3 Lubricant compositions according to the invention and comparative ones *comprising detergents, dispersants, antioxidants and anti-wear agents. LC7 CC3 CC4 (% by (% by (% by Lubricant composition weight) weight) weight) triethylcitrate 1 — — Organic friction modifier 0.5 — 0.5 according to the invention Additive package 2* 10.7 10.9 10.8 Viscosity index improver 5.8 5.9 5.9 (acrylic polymers) Group III and IV base oils 82 83.2 82.8

Example 2: Tribological Test Results

The tribological tests were carried out under the following conditions:

TABLE 4 Tribological test conditions Slip-slip Filler 30N (0.96 Gpa) Temperature 100° C. SRR 50% Entrainment speed 0.1 m/s Time (min) 5 15 30 60 120 Stribeck Filler 30N (0.96 Gpa) Temperature 100° C. SRR 50% Entrainment speed 3 to 0.007 m/s

The coefficient of friction of the lubricant compositions tested is determined at 100° C. using an MTM (Mini Traction Machine) device using a 2 cm diameter hardened steel ball on a hardened steel plane.

The MTM device can be a PCS Instruments device. This device allows a steel ball and a steel plane to be moved relative to each other in order to determine the coefficients of friction for a given lubricant composition while varying various properties such as speed, load, and temperature.

The hardened steel plane is AISI 52100 with a mirror finish (Ra less than 0.01 μm) and the ball is also AISI 52100 made of hardened steel.

The applied load is 30 N (0.96 Gpa) and the rotation speed varies from 0.007 m/s to 3 m/s.

Approximately 50 ml of the tested lubricant composition was introduced into the device. The ball is engaged face to face with the plane, said ball and plane being independently actuated so as to create a mixed rolling/sliding contact.

The coefficient of friction is measured and recorded by means of a force sensor.

The test is conducted for a duration of 121 minutes (alternating between slip-slip and Stribeck periods). The velocity is initially held constant at 0.1 m/s and at each interval defined in the table, the velocity is increased from 3 to 0.007 m/s for one minute before returning to a velocity of 0.1 m/s at the end of said defined period.

The coefficient of friction is thus measured as a function of the defined speed.

Table 5 gives the results for the compositions in Table 2, expressed in terms of coefficient of friction versus slip speed.

TABLE 5 Speed of Speed of 0.01 m/s 0.1 m/s Coefficient of friction CC1 0.068 0.070 Coefficient of friction CC2 0.133 0.112 Coefficient of friction LC1 0.040 0.040 Coefficient of friction LC2 0.022 0.021 Coefficient of friction LC3 0.050 0.061 Coefficient of friction LC4 0.048 0.047 Coefficient of friction LC5 0.040 0.041

Table 6 gives the results for the compositions in Table 3, expressed in terms of the coefficient of friction as a function of slip speed.

TABLE 6 Speed of Speed of 0.01 mm/s 0.1 mm/s Coefficient of friction LC7 0.073 0.065 Coefficient of friction CC3 0.131 0.115 Coefficient of friction CC4 0.142 0.122

The results show that:

-   -   the value of the coefficient of friction does not depend         significantly on the polymeric friction modifier and/or ester         content.     -   the ester has no significant effect on the coefficient of         friction when used alone, without a polymeric friction modifier.     -   there is a synergy between the ester defined herein and the         polymeric friction modifiers within the lubricant composition to         significantly decrease the coefficient of friction and therefore         to limit friction between mechanical parts. 

1. A lubricant composition comprising, based on the total weight of lubricant composition: at least one base oil; 0.005 to 10% by weight of at least one polymeric organic friction modifier; and 0.005 to 10% by weight of at least one ester which is a product of the esterification reaction between a saturated or unsaturated, linear, cyclic or branched monohydric alcohol having 1 to 10 carbon atoms and a carboxylic polyacid or between a linear, cyclic or branched polyol and a saturated or unsaturated, linear, cyclic or branched monocarboxylic acid having between 1 and 10 carbon atoms, said polymeric organic friction modifier being the reaction product of: a) at least one hydrophobic polymer subunit which comprises a hydrophobic polymer selected from polyolefins, polyacrylics and polystyrenes; b) at least one hydrophilic polymer subunit which comprises a hydrophilic polymer selected from polyethers, polyesters and polyamides; c) optionally at least one backbone moiety capable of linking polymeric subunits together; and d) optionally a chain termination group.
 2. The composition according to claim 1, wherein the polymeric organic friction modifier has a weight average molecular weight of from 1000 to 30,000 Daltons.
 3. The composition according to claim 1, wherein the organic friction modifier is the reaction product of a functionalised polyolefin, a polyether, a polyol and a carboxylic acid end group.
 4. The composition according to claim 1, wherein the ester is selected from: a triester of glycerol and of a monocarboxylic acid having from 1 to 10 carbon atoms; and a triester of citric acid and of a monohydric alcohol having from 1 to 10 carbon atoms; and mixtures thereof.
 5. The composition according to claim 1, wherein the ester is selected from glycerol triheptanoate, triethylcitrate, tributylcitrate and mixtures thereof.
 6. The composition according to claim 1, at least 50% by weight of one or more base oils; from 0.005 a 10% by weight of one or more polymeric organic friction modifiers; from 0.005 to 10% by weight of one or more esters selected from glycerol esters, citric acid esters, tartaric acid esters and mixtures thereof; optionally from 0.005 to 30% by weight of one or more functional additives other than polymeric organic friction modifiers and glycerol esters, citric acid esters and tartaric acid esters
 7. A method for reducing friction between two mechanical parts, comprising one step of bringing the two mechanical parts into contact with the lubricating composition according to claim
 1. 8. The method according to claim 7 for reducing the wear of parts
 9. A method for lubricating mechanical parts, comprising at least one step of bringing a part into contact with the lubricating composition according to claim
 1. 